Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Celestron C90 Orange Tube Original LAR + Diagonal Recommendations

  • Please log in to reply
5 replies to this topic

#1 topgun0728

topgun0728

    Lift Off

  • -----
  • topic starter
  • Posts: 2
  • Joined: 29 Apr 2021

Posted 29 April 2021 - 06:03 PM

Howdy!

 

I have read quite a bit of literature here about the nifty Celestron C90 Orange Tube and the proverbial "hen's teeth" original LAR.

 

Well, I pulled the trigger on a mint condition C90 Orange Tube recently that managed to come with an original LAR and Celestron 93653-A 1.25-Inch Visual Back (made in Japan version).

 

When it comes to diagonals, do you folks (especially those with actual experience owning the C90 Orange Tube) recommend investing in a good quality 2-inch SCT diagonal (e.g. a GSO Quartz 99%) to screw onto the LAR directly or investing in a good quality 1.25-Inch diagonal (e.g. a dielectric) to screw onto the Visual Back?

 

I plan to only use 1.25-inch eye pieces so perhaps a 2-inch SCT diagonal is overkill (I found a picture on the internet of someone using this setup with a 2-inch eye piece and though it would be fun to give it a try since I do have the original LAR). Also, has anyone been able to use a 2-inch SCT diagonal with the C90 and get 1.25-inch eye pieces to focus properly? I read about issues with focusing the C90 with using modern diagonals and eye pieces over the original 0.965-inch accessories.

 

Another thought I have is to use the Orion 90-Degree Correct-Image diagonal with the Visual Back, but I am not sure about how the optical quality would stack up against a 1.25-inch dielectric or a 2-inch GSO Quartz 99%. There is basically only 1 model of the 90-degree correct-image diagonal (handy for terrestrial use), so no choices there in terms of upgrades.

 

Also, for those who have tried a hybrid diagonal versus either a 1.25-inch diagonal screwed into the Visual Back or a 2-inch SCT diagonal (probably rare) screwed into the LAR directly, do you actually notice any optical improvements when using 1.25-inch eye pieces? The 0.965-inch hole is the bottleneck here and I am not sure exactly how much of an optical improvement one can really squeeze out of this little orange tube.

 

Thanks in advance!


Edited by topgun0728, 29 April 2021 - 06:05 PM.

  • shooze likes this

#2 shooze

shooze

    Vostok 1

  • *****
  • Posts: 138
  • Joined: 09 Dec 2016
  • Loc: Ontario, Canada

Posted 29 April 2021 - 06:50 PM

Howdy!

 

I have read quite a bit of literature here about the nifty Celestron C90 Orange Tube and the proverbial "hen's teeth" original LAR.

 

Well, I pulled the trigger on a mint condition C90 Orange Tube recently that managed to come with an original LAR and Celestron 93653-A 1.25-Inch Visual Back (made in Japan version).

 

When it comes to diagonals, do you folks (especially those with actual experience owning the C90 Orange Tube) recommend investing in a good quality 2-inch SCT diagonal (e.g. a GSO Quartz 99%) to screw onto the LAR directly or investing in a good quality 1.25-Inch diagonal (e.g. a dielectric) to screw onto the Visual Back?

 

I plan to only use 1.25-inch eye pieces so perhaps a 2-inch SCT diagonal is overkill (I found a picture on the internet of someone using this setup with a 2-inch eye piece and though it would be fun to give it a try since I do have the original LAR). Also, has anyone been able to use a 2-inch SCT diagonal with the C90 and get 1.25-inch eye pieces to focus properly? I read about issues with focusing the C90 with using modern diagonals and eye pieces over the original 0.965-inch accessories.

 

Another thought I have is to use the Orion 90-Degree Correct-Image diagonal with the Visual Back, but I am not sure about how the optical quality would stack up against a 1.25-inch dielectric or a 2-inch GSO Quartz 99%. There is basically only 1 model of the 90-degree correct-image diagonal (handy for terrestrial use), so no choices there in terms of upgrades.

 

Also, for those who have tried a hybrid diagonal versus either a 1.25-inch diagonal screwed into the Visual Back or a 2-inch SCT diagonal (probably rare) screwed into the LAR directly, do you actually notice any optical improvements when using 1.25-inch eye pieces? The 0.965-inch hole is the bottleneck here and I am not sure exactly how much of an optical improvement one can really squeeze out of this little orange tube.

 

Thanks in advance!

Here is my C-90 with the 1.25" visual back and diagonal.

 

IMG 9943
IMG 9937
IMG 9955

  • Bomber Bob likes this

#3 stomias

stomias

    Explorer 1

  • ****-
  • Posts: 99
  • Joined: 02 Jan 2015

Posted 29 April 2021 - 07:38 PM

I have the LAR and this adapter that screws on to it and accepts 2" accessories. Had it for years. Probably got it from Orion.

 
DSC 7835 copy
 
DSC 7836 copy

  • Bomber Bob likes this

#4 Terra Nova

Terra Nova

    ISS

  • *****
  • Posts: 24,839
  • Joined: 29 May 2012
  • Loc: 39.07°N, 229m AMSL, USA

Posted 29 April 2021 - 07:50 PM

Definitely don’t go for an RACI diagonal. It will degrade the optical quality of your images and you will see an annoying light bar across the field when you look at bright objects due to internal reflections along the seam where the two prisms are glued together. A good mirror diagonal is fine as is a prismatic star diagonal. There is really no point in going with a two inch diagonal because the hole in the back that goes through the primary mirror is much smaller and you won’t be able to take advantage of it.



#5 topgun0728

topgun0728

    Lift Off

  • -----
  • topic starter
  • Posts: 2
  • Joined: 29 Apr 2021

Posted 29 April 2021 - 11:45 PM

Thanks so much for the helpful replies! Does the "annoying light bar" apply to the 90-Degree Correct-Image diagonal as well as the 45-degree version (typical)? I actually don't know how they came up with the 90-Degree Correct-Image diagonal as it doesn't make sense to me. Not sure how Orion managed to made a 90-degree version when many other manufacturers can only make the 45-degree version with small apertures (much smaller than a standard 1.25-inch diagonal).

 

Shooze - Your setup looks great! Does this offer a big optical improvement over a hybrid diagonal? GSO actually makes a nice 99% dielectric hybrid diagonal and some folks have reported that the set screw on the C90 is too short to hold the diagonal in place. I tried the diagonal on mine and it works fine, but I am hoping that going with the LAR + 1.25-inch Visual Back + a nice quality 1.25-inch diagonal would offer an optical improvement over a hybrid diagonal (assuming no focusing issues).



#6 Terra Nova

Terra Nova

    ISS

  • *****
  • Posts: 24,839
  • Joined: 29 May 2012
  • Loc: 39.07°N, 229m AMSL, USA

Posted 30 April 2021 - 10:59 AM

Thanks so much for the helpful replies! Does the "annoying light bar" apply to the 90-Degree Correct-Image diagonal as well as the 45-degree version (typical)? I actually don't know how they came up with the 90-Degree Correct-Image diagonal as it doesn't make sense to me. Not sure how Orion managed to made a 90-degree version when many other manufacturers can only make the 45-degree version with small apertures (much smaller than a standard 1.25-inch diagonal).

Yes! Zeiss (and Baader/Zeiss) is the only correct-image diagonal (or turret) that I know of that doesn’t. But you will pay dearly for that! They are far from inexpensive.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics